Radio frequency transmission system



H. PRATT RADIO FREQUENCY TRANSMISSION SYSTEM May 8, 1923. 1,454,652

Filed NOV. 22 1921 WITNESS INVENTOR ATTORNEYS Patented ay 8, 123.

DEN PRATT, OF SAN FRANCISCO, CALIFORNIA, ASSIGNOR TO AUGUSTUS TAYLOR,

OF SAN FRANCISCO, CALIFORNIA.

RADIO FREQUENCY TRANSMISSION SYSTEM.

Application filed November 22, 1921.

To all whom it may mm Be it known that I, HARADEN PRATT, a citizen of the United States, and residing at the city and county of San Francisco, State of California, have invented a certain new and useful Radio Fr uency Transmission System, of which the ollowing is a specification.

My invention relates to a radio frequency transmission system, and more particularly to a system embodying a source of high frequency oscillations, such as a Poulsen are,

which may under certain conditions produce objectionable higher harmonic oscillations. These higher harmonics not only produce an energy loss, but they also present a problem of interference with stations tuned near the frequencies of the higher harmonics. As the number of stations increase, this interference becomes more and more objectionable, and it becomes not only advantageous to suppress the higher harmonics, but almost imperative to do so. One of the objects of my invention is to make it possible to suppress substantially all of the higher harmonics by means of a simple and inexpensive arrangement of circuits.

The invention possesses other advantageous features, some of which, with the foregoing, will beset forth at length in the following description, where I shall outline in full that form of the invention which I have selected for illustration in the drawings accompanying and forming part of the present specification. In the drawings, I have shown a single embodiment of my invention, but it is to be understood that I do not limit myself to this form, since the invention as expressed inthe claims may be embodied in a plurality of forms.

Referring to the drawings, the single figure represents a wiring diagram of one form of circuits embodying my invention.

In this figure, the means for producing high frequency current is shown as an arc converter comprising the are 1, fed from a source 2 of direct current or of low frequency current, through the usual choke coils 3, 4. These coils may also serve to pro duce the magnetic field influencing the are in the well known manner. The high frequency oscillations may be made use of to supply an antenna circuit consisting of the antenna 5, inductor 6 and a grounded conductor 7. In series with the antenna circuit Serial No. 516,912.

are so chosen that they form a resonant circuit for the frequency of transmission, by themselves or in conjunction with any por tion of the antenna circuit. In the present instance that portion of the circuit including the arc l, reactance 8 and reactance 9, is so tuned. Thus, for the fundamental or required frequency, the points 10 and 11 located at the terminals of the tuned portion have a minimum potential drop, since the reactances neutralize each other, and the only E. M. F. obtained is a small amount corresponding to the resistance drop. For any other frequency but that required, the potential drop between points 10 and 11 is greater, because the reactances no longer neutralize or balance each other.

In order to keep the higher harmonic currents out of the antenna, it is possible to connect a branch circuit across points 10 and 11 that will by-pass or absorb currents of all frequencies except that required for trans mission. In the present instance, I show a scheme for by-passing the objectionable frequency currents through a circuit connected across points 10 and 11. The circuit may be so arranged-that even if an E. M. F. be present across points 10 and 11 of the required frequency, it could find no path through this circuit to drive a current. This may be accomplished by the use of a condenser 12 and inductive reactance 13 placed in parallel and then directly across the points 10 and 11 by means of the conductors 14 and 15. The condenser 12 is so proportioned that it has the same value of reactance as the inductance 13, at the required frequency. If this condition is fulfilled, it is readily seen that any current roduced in the condenser circuit by the E. F. across points 10 and 11 is exactly equal and opposite to the current produced by the same E. M. F. in the inductive reactance circuit. The net result is that there is zero current in the conductors 14C and 15; thus no current of the required frequency is by-passed. For any other frequency, however, the condition of balance between the condenser current and the inductance coil current does not hold, and some current exists in the conductors 14 and 15. Thus, a maximum impedance for the required frequency current is obtained,

are

Several advantages of the circuit diagram shown may here be enumerated. Direct current or low frequency current from the source 2 is prevented from circulating through the inductive reactance 13 by the condenser 9. Furthermore, the condenser 12 may be inexpensively constructed, since it handles only the higher harmonic currents which are relatively of low amplitude.

I claim:

1. In a radio frequency system, a source for generating high frequency oscillations, a load circuit connected in series with the source, a plurality of elements in series with the load circuit and the source, for producing across the terminals of the elements in series a minimum potential drop for the frequency it is desired to use, and a circuit connected directly across the terminals having a maximum impedance for the said frequency.

2. In a radio frequency system, a source for generating high frequency oscillations, a load circuit connected in series with the source, a plurality of impedance devices connected in series with the load circuit and the source, said devices being so proportioned that a minimum potential drop for the frequency it is desired to use exists across the two points corresponding to the terminals of the devices in series, and a circuit directly connected across these two points, said circuit having a capacitive reactance and an inductive reac'tance in parallel, said reactances being so proportioned that this branch circuit has a maximum impedance for currents of the said frequency, these reactances in said branch circuit comprising all of the reactances therein.

In testimony whereof, I have hereunto set my hand.

' HARADEN PRATT. 

